A cord passing over a frictionless, massless pulley has a 4 kg object tied to one end and a 21 kg tied to the other. Compute the magnitude of the acceleration in the cord.

Answer 1

If T = the tension in the cord, then the equations are as follows if a = the acceleration, s = seconds

Perform a force balance on each string section for the masses:

For the 4kg mass: T - (4kg)(9.8m/s²) = (4kg)a

For the 21 kg mass: T - (21kg)(9.8m/s²) = -(21kg)a

Eliminating T from both equations you find that a = 6.664 m/s²